Rechargeable battery cell

ABSTRACT

This disclosure relates to a rechargeable battery cell having an active metal, at least one positive electrode, at least one negative electrode, a housing and an electrolyte, the positive electrode comprising at least one compound in the form of a layered oxide as an active material and the electrolyte being based on SO2 and comprising at least one first conducting salt which has the formula (I),M being a metal selected from the group formed by alkali metals, alkaline earth metals, metals of group 12 of the periodic table of the elements, and aluminum; x being an integer from 1 to 3; the substituents R1, R2, R3 and R4 being selected independently of one another from the group formed by C1-C10 alkyl, C2-C10 alkenyl, C2-C10 alkynyl, C3-C10 cycloalkyl, C6-C14 aryl and C5-C14 heteroaryl; and Z being aluminum or boron.

RELATED APPLICATIONS

This application is a continuation of PCT/EP2020/071565, filed Jul. 30,2020, which claims priority to EP 19 189 435.1, filed Jul. 31, 2019, theentire disclosures of both of which are hereby incorporated herein byreference.

BACKGROUND

This disclosure relates to a rechargeable battery cell having anSO₂-based electrolyte.

Rechargeable battery cells are of great importance in many technicalfields. They are often used for applications which require only smallrechargeable battery cells having relatively low current intensities,for example, for the operation of cell phones. In addition, there isalso a great need for larger rechargeable battery cells for high-energyapplications, with mass storage of energy in the form of battery cellsbeing of particular importance for the electric propulsion of vehicles.

High energy density is an important requirement for these types ofrechargeable battery cells. This means that the rechargeable batterycell should contain as much electrical energy as possible per unitweight and volume. Lithium has proven to be particularly advantageous asan active metal for this purpose. The active metal of a rechargeablebattery cell is the metal whose ions within the electrolyte migrate tothe negative or positive electrode when the cell is being charged ordischarged and participate in electrochemical processes there. Theseelectrochemical processes lead directly or indirectly to the release ofelectrons into the external circuit or to the absorption of electronsfrom the external circuit. Rechargeable battery cells comprising lithiumas an active metal are also referred to as lithium-ion cells. The energydensity of these lithium-ion cells can either be increased by increasingthe specific capacity of the electrodes or by increasing the cellvoltage.

Both the positive and negative electrodes of lithium-ion cells aredesigned as insertion electrodes. The term “insertion electrode” in thesense of this disclosure refers to electrodes which have a crystalstructure into which ions of the active material can be stored andremoved during operation of the lithium-ion cell. This means that theelectrode processes can take place not only on the surface of theelectrodes, but also within the crystalline structure. Both electrodestypically have a thickness of less than 100 μm and are therefore verythin. When charging the lithium-ion cell, the ions of the active metalare removed from the positive electrode and stored in the negativeelectrode. The reverse process takes place when the lithium-ion cell isdischarged.

The electrolyte is also an important functional element of everyrechargeable battery cell. It usually comprises a solvent or a solventblend and at least one conducting salt. Solid electrolytes or ionicliquids, for example, do not comprise a solvent, but only a conductingsalt. The electrolyte is in contact with the positive and negativeelectrodes of the battery cell. At least one ion of the conducting salt(anion or cation) is sufficiently mobile in the electrolyte such that acharge transport between the electrodes, required for the functioning ofthe rechargeable battery cell, can take place through ionic conduction.The electrolyte is oxidatively electrochemically decomposed from acertain upper cell voltage of the rechargeable battery cell. Thisprocess often leads to an irreversible destruction of the electrolytecomponents, and thus to a failure of the rechargeable battery cell.Reductive processes can also decompose the electrolyte when fallingbelow a certain cell voltage. In order to avoid these processes, thepositive and negative electrodes are chosen such that the cell voltageis below or above the decomposition voltage of the electrolyte. Theelectrolyte thus determines the voltage window, in the range of which arechargeable battery cell can be operated reversibly, that is,repeatedly charged and discharged.

The lithium-ion cells known from the prior art comprise an electrolyteconsisting of an organic solvent or solvent blend and a conducting saltdissolved therein. The conducting salt is a lithium salt such as lithiumhexafluorophosphate (LiPF₆). The solvent blend can comprise, forexample, ethylene carbonate. The electrolyte LP57, which has thecomposition 1 M LiPF₆ in EC:EMC 3:7, is an example of such anelectrolyte. Due to the organic solvent or solvent blend, these kinds oflithium ion cells are also referred to as organic lithium-ion cells.

The negative electrode of these organic lithium-ion cells consists of acarbon coating which is applied to a discharge element made of copper.The discharge element provides the electronically conductive connectionrequired between the carbon coating and the external circuit. Thepositive electrode consists of lithium cobalt oxide (LiCoO₂), which isapplied to a discharge element made of aluminum.

It has long been known that unintentional overcharging of organiclithium ion cells leads to the irreversible decomposition of electrolytecomponents. The oxidative decomposition of the organic solvent and/orthe conducting salt takes place on the surface of the positiveelectrode. The reaction heat generated during this decomposition and theresulting gaseous products are responsible for the subsequent so-called“thermal runaway” and the resulting destruction of the organic lithiumion cell. The vast majority of charging protocols for these organiclithium-ion cells use the cell voltage as an indicator of the end ofcharging. Accidents caused by the thermal runaway are particularlylikely to occur when using multi-cell battery packs in which a pluralityof organic lithium-ion cells having dissimilar capacities are connectedin series.

Organic lithium-ion cells are therefore problematic in terms of theirstability and long-term operational reliability. Safety risks are alsocaused in particular by the flammability of the organic solvent orsolvent blend. When an organic lithium-ion cell catches fire or evenexplodes, the organic solvent in the electrolyte forms a combustiblematerial. Additional measures must be taken to avoid such safety risks.These measures include, in particular, a very precise regulation of thecharging and discharging processes of the organic lithium-ion cell andan optimized battery design. Furthermore, the organic lithium-ion cellcomprises components which melt in the event of an unintentionalincrease in temperature and can thereby flood the organic lithium-ioncell with molten plastic. A further uncontrolled increase in temperatureis thus prevented. However, these measures lead to increased productioncosts in the manufacture of the organic lithium-ion cell and to anincreased volume and weight. Furthermore, these measures reduce theenergy density of the organic lithium-ion cell.

A further disadvantage of organic lithium-ion cells is that anyhydrolysis products produced in the presence of residual amounts ofwater are very aggressive towards the cell components of therechargeable battery cell. For example, the conducting salt LiPF₆, whichis often used in organic cells, produces very reactive, aggressivehydrogen fluoride (HF) through reaction with traces of water. Because ofthis, when manufacturing such rechargeable battery cells having anorganic electrolyte, attention must be paid to minimizing the residualwater content comprised in the electrolyte and the cell components.Production therefore often takes place in costly drying rooms underextremely low humidity. The issues described above regarding stabilityand long-term operational reliability are of particular importance forthe development of organic lithium-ion cells, which, on the one hand,are characterized by a high energy and power density level, and, on theother hand, by a very high degree of operational reliability and a verylong service life, including a particularly high number of usable chargeand discharge cycles.

In order to increase the energy density of organic lithium-ion cells,new cathode materials were tested in the prior art, that is, newmaterials for positive electrodes which can be cycled with a higherend-of-charge voltage, that is, a higher upper potential. Such materialsare, for example, lithium nickel manganese cobalt oxides, which are alsoreferred to as NMC for short. The following publication reports on it:

-   -   “Oxygen Release and Its Effect on the Cycling Stability of        LiNi_(x)Mn_(y)Co_(z)O₂ (NMC) Cathode Materials for Li-Ion        Batteries”    -   Roland Jung; Michael Metzger; Filippo Maglia; Christoph Stinner        and Hubert A. Gasteigera. Journal of The Electrochemical        Society, 164 (7) A1361-A1377 (2017)

This publication by Jung et al. is referred to below as [V1]. Jung etal. tested various NMC materials having the composition NMC(xyz) in[V1]. The lowercase letters (xyz) in brackets specify the indices x, yand z of the compound LiNi_(x)Mn_(y)Co_(z)O₂. In [V1], three differentNMC cathode materials were cycled in an organic lithium-ion cell havingthe previously described LP57 electrolyte (1 M LiPF₆ in EC:EMC 3:7)using different end-of-charge voltages. The end-of-charge voltage is thevoltage up to which an individual battery cell or a battery made of aplurality of battery cells is charged with the aid of a battery charger.The batteries are often charged with a certain charge current intensityup to a certain upper potential, that is, up to the end-of-chargevoltage. The corresponding upper potential is held until the chargecurrent has dropped to a certain value. 300 charge/discharge cycles wererespectively performed in [V1]. Table 1 below shows the reduction in thedischarge capacity of the 5th cycle compared to the 300th. cyclespecified in %.

TABLE 1 Discharge Capacities with Increasing End-of-Charge Voltages from[V1] by Jung et al. 4.0 V 4.2 V 4.4 V 4.6 V Discharge DischargeDischarge Discharge Material Capacity [%]: Capacity [%]: Capacity [%]:Capacity [%]: NMC(111) — 93% 94% 42% NMC(622) — 95% 94% 39% NMC(811) 90%77% 66% —

Table 1 shows that with materials NMC (111) and NMC (622), there is adrastic decrease in capacity when cycling with an end-of-charge voltageof 4.6 volts, because only 42% and 39% of the original capacity areachieved. The material NMC (811) was only cycled up to 4.4 volts,wherein a steady decrease in capacity with increasing end-of-chargevoltage was also observed. On the basis of [V1], it can therefore bedetermined that organic lithium-ion cells having the NMC cathodematerials can be cycled at a higher upper potential. The disadvantage,however, is that there is an undesirably high decrease in capacity.

A further development known from prior art therefore provides for theuse of an electrolyte based on sulfur dioxide (SO₂) instead of anorganic electrolyte for rechargeable battery cells. Rechargeable batterycells, which comprise an SO₂-based electrolyte, exhibit, among otherthings, high ionic conductivity. The term “SO₂-based electrolyte” in thesense of this disclosure refers to an electrolyte which comprises SO₂not merely as an additive at low concentrations, but in which themobility of the ions in the conducting salt, which is comprised in theelectrolyte and which causes the charge transport, is at least in part,largely or even completely ensured by SO₂. The SO₂ thus serves as asolvent for the conducting salt. The conducting salt can form a liquidsolvate complex with the gaseous SO₂, whereby the SO₂ is bound and thevapor pressure is noticeably reduced compared to the pure SO₂.Electrolytes having low vapor pressure are produced. Compared to theorganic electrolytes described above, these SO₂-based electrolytes havethe advantage of being non-combustible. Safety risks, which might occurdue to the electrolyte's flammability, can thus be excluded.

For example, EP 1 201 004 B1 discloses an SO₂-based electrolyte havingthe composition LiAlCl₄*SO₂ in combination with a positive electrodemade of LiCoO₂ (hereinafter referred to as [V2]). [V2] suggests the useof an additional salt to avoid disruptive decomposition reactions, suchas the undesired formation of chlorine (Cl₂) from lithiumtetrachloroaluminate (LiAlCl₄), when the rechargeable battery cell isovercharged from an upper potential of 4.1 to 4.2 volts.

EP 2534719 B1 (hereinafter referred to as [V3]) also discloses anSO₂-based electrolyte having, among other things, LiAlCl₄ as theconducting salt. For example, said LiAlCl₄ forms complexes of theformula LiAlCl₄*1.5 mol SO₂ or LiAlCl₄*6 mol SO₂ with the SO₂. Lithiumiron phosphate (LiFePO₄) is used as the positive electrode in [V3].LiFePO₄ has a lower end-of-charge voltage (3.7 V) compared to LiCoO₂(4.2 V). The problem of undesired overcharging reactions does not arisein this rechargeable battery cell, since upper potentials of 4.1 volts,which are harmful to the electrolyte, are not reached. A disadvantagethat also occurs, among other things, with these SO₂-based electrolytesis that any hydrolysis products formed in the presence of residualamounts of water react with the cell components of the rechargeablebattery cell and thus lead to the formation of undesired by-products.Because of this, in the manufacture of such rechargeable battery cellshaving an SO₂-based electrolyte, attention should be paid to minimizingthe residual water content comprised in the electrolyte and the cellcomponents.

A further problem with the SO₂-based electrolytes is that manyconducting salts, in particular also known for organic lithium-ioncells, are not soluble in SO₂. Measurements showed that SO₂ is a poorsolvent for many conducting salts, such as lithium fluoride (LiF),lithium bromide (LiBr), lithium sulfate (Li₂SO₄), lithiumbis(oxalato)borate (LiBOB), lithium hexafluoroarsenate (LiAsF₆), lithiumtetrafluoroborate (LiBF₄), trilithium hexafluoroaluminate (Li₃AlF₆),lithium hexafluoroantimonate (LiSbF₆), lithium difluoro(oxalato)borate(LiBF₂C₂O₄), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI),lithium metaborate (LiBO₂), lithium aluminate (LiAlO₂), lithium triflate(LiCF₃SO₃) and lithium chlorosulfonate (LiSO₃Cl). The solubility ofthese conducting salts in SO₂ is approx. 10⁻²-10⁻⁴ mol/L (see Table 2).With these low salt concentrations, it can be assumed that there are atmost only low conductivities, which are not sufficient for the usefuloperation of a rechargeable battery cell.

TABLE 2 Solubility of various salts in SO₂ Conducting Solubility/mol/Conducting Solubility/mol/ salt L in SO₂ salt L in SO₂ LiF 2.1 · 10⁻³LiPF₆ 1.5 · 10⁻² LiBr 4.9 · 10⁻³ LiSbF₆ 2.8 · 10⁻⁴ Li₂SO₄ 2.7 · 10⁻⁴LiBF₂(C₂O₄) 1.4 · 10⁻⁴ LiB(C₂O₄)₂ 3.2 · 10⁻⁴ CF₃SO₂NLiSO₂CF₃ 1.5 · 10⁻²Li₃PO₄ — LiBO₂ 2.6 · 10⁻⁴ Li₃AlF₆ 2.3 · 10⁻³ LiAlO₂ 4.3 · 10⁻⁴ LiBF₄ 1.7· 10⁻³ LiCF₃SO₃ 6.3 · 10⁻⁴ LiAsF₆ 1.4 · 10⁻³

In order to further improve the possible uses and properties ofrechargeable battery cells that comprise an SO₂-based electrolyte, theobject of this disclosure is to specify a rechargeable battery cellhaving an SO₂-based electrolyte, which, compared to the rechargeablebattery cells known from the prior art:

-   -   has a wide electrochemical window, so that no oxidative        electrolyte decomposition occurs at the positive electrode;    -   has a stable coating layer on the negative electrode, whereby        the coating layer capacity should be low and no further        reductive electrolyte decomposition should occur on the negative        electrode during further operation;    -   comprises an SO₂-based electrolyte which exhibits good        solubility for conducting salts and is therefore a good ion        conductor and electronic insulator, so that ion transport can be        facilitated and self-discharge can be reduced to a minimum;    -   comprises an SO₂-based electrolyte that is also inert to other        components of the rechargeable battery cell, such as separators,        electrode materials and cell packaging materials;    -   is resistant against various misuses such as electrical,        mechanical or thermal;    -   comprises an SO₂-based electrolyte, which exhibits an increased        stability against residual amounts of water in the cell        components of rechargeable battery cells;    -   exhibits improved electrical performance data, in particular        high energy density;    -   has improved overcharging and deep discharging and less        self-discharge and    -   shows an increased service life, in particular a high number of        usable charge and discharge cycles.

Such rechargeable battery cells should, in particular, also have verygood electrical energy and performance data, high operationalreliability and service life, in particular a large number of usablecharge and discharge cycles, without the electrolyte decomposing duringoperation of the rechargeable battery cell.

SUMMARY

A rechargeable battery cell according to this disclosure comprises anactive metal, at least one positive electrode, at least one negativeelectrode, a housing and an electrolyte. The positive electrodecomprises at least one compound in the form of a layered oxide as anactive material. The electrolyte is based on SO₂ and comprises at leastone first conducting salt. Said first conducting salt has the formula(I).

In formula (I), M is a metal selected from the group formed by alkalimetals, alkaline earth metals, metals of group 12 of the periodic tableof the elements and aluminum. x is an integer from 1 to 3. Thesubstituents R¹, R², R³ and R⁴ are selected independently of one anotherfrom the group formed by C₁-C₁₀ alkyl, C₂-C₁₀ alkenyl, C₂-C₁₀ alkynyl,C₃-C₁₀ cycloalkyl, C₆-C₁₄ aryl and C₅-C₁₄ heteroaryl. The central atom Zis either aluminum or boron.

In the sense of this disclosure, the term “layered oxides” refers tometal oxides which are derived from the α-NaFeO₂ structure type. In thisstructure type, the oxygen atoms occupy the lattice positions of aface-centered cubic lattice (so-called fcc lattice), in which the metalions occupy the octahedral holes that are present.

The SO₂-based electrolyte used in the rechargeable battery cellaccording to this disclosure comprises SO₂ not only as an additive inlow concentration, but in concentrations at which the mobility of theions of the first conducting salt, which is comprised in the electrolyteand causes the charge transport, is at least partially, largely or evencompletely ensured by the SO₂. The first conducting salt is dissolved inthe electrolyte and shows very good solubility therein. It can form aliquid solvate complex with the gaseous SO₂, in which the SO₂ is bound.In this case, the vapor pressure of the liquid solvate complex isnoticeably reduced compared to the pure SO₂, producing electrolytes thathave a low vapor pressure. However, it is also within the scope of thisdisclosure that, depending on the chemical structure of the firstconducting salt according to formula (I), no reduction in vapor pressurecan occur in the production of the electrolyte according to thisdisclosure. In the last-mentioned case, it is preferred for theproduction of the electrolyte according to this disclosure to be carriedout at low temperature or under pressure. The electrolyte may alsocomprise a plurality of conducting salts of the formula (I), whichdiffer from one another in their chemical structure.

In the sense of this disclosure, the term “C₁-C₁₀ alkyl” includes linearor branched saturated hydrocarbon groups having one to ten carbon atoms.These include, in particular, methyl, ethyl, n-propyl, isopropyl,n-butyl, sec-butyl, iso-butyl, tert-butyl, n-pentyl, iso-pentyl,2,2-dimethylpropyl, n-hexyl, iso-hexyl, 2-ethylhexyl, n-heptyl,iso-heptyl, n-octyl, iso-octyl, n-nonyl, n-decyl and the like.

In the sense of this disclosure, the term “C₂-C₁₀ alkenyl” includesunsaturated linear or branched hydrocarbon groups having two to tencarbon atoms, wherein the hydrocarbon groups have at least one C—Cdouble bond. These include, in particular, ethenyl, 1-propenyl,2-propenyl, 1-n-butenyl, 2-n-butenyl, isobutenyl, 1-pentenyl, 1-hexenyl,1-heptenyl, 1-octenyl, 1-nonenyl, 1-decenyl and the like.

In the sense of this disclosure, the term “C₂-C₁₀ alkynyl” includesunsaturated linear or branched hydrocarbon groups having two to tencarbon atoms, wherein the hydrocarbon groups have at least one C—Ctriple bond. This includes, in particular, ethynyl, 1-propynyl,2-propynyl, 1-n-butynyl, 2-n-butynyl, isobutynyl, 1-pentynyl, 1-hexynyl,1-heptynyl, 1-octynyl, 1-nonynyl, 1-decynyl, and the like.

In the sense of this disclosure, the term “C₃-C₁₀ cycloalkyl” includescyclic, saturated hydrocarbon groups having three to ten carbon atoms.These include, in particular, cyclopropyl, cyclobutyl, cyclopentyl,cyclohexyl, cycloheptyl, cyclohexyl, cyclononyl and cyclodecanyl.

In the sense of this disclosure, the term “C₆-C₁₄ aryl” includesaromatic hydrocarbon groups having six to fourteen ring carbon atoms.This includes, in particular, phenyl (C₆H₅ group), naphthyl (C₁₀H₇group) and anthracyl (C₁₄H₉ group).

In the sense of this disclosure, the term “C₅-C₁₄ heteroaryl” includesaromatic hydrocarbon groups having five to fourteen ring hydrocarbonatoms in which at least one hydrocarbon atom is replaced by a nitrogen,oxygen or sulfur atom. These include, in particular, pyrrolyl, furanyl,thiophenyl, pyridinyl, pyranyl, thiopyranyl and the like. All of thehydrocarbon groups mentioned above are each bonded to the central atomaccording to formula (I) via the oxygen atom.

A rechargeable battery cell having such an electrolyte has the advantageover rechargeable battery cells having electrolytes known from the priorart in that the first conducting salt comprised therein has higheroxidation stability and consequently shows essentially no decompositionat higher cell voltages. Said electrolyte is resistant to oxidation,preferably at least up to an upper potential of 4.0 volts, morepreferably at least up to an upper potential of 4.2 volts, morepreferably at least up to an upper potential of 4.4 volts, morepreferably at least up to an upper potential of 4.6 volts, morepreferably at least up to an upper potential of 4.8 volts and mostpreferably at least up to an upper potential of 5.0 volts. Thus, whenusing such an electrolyte in a rechargeable battery cell, there islittle or no electrolyte decomposition within the working potentials,that is, in the range between the end-of-charge voltage and theend-of-discharge voltage of both electrodes of the rechargeable batterycell. As a result, rechargeable battery cells, for example, can have anend-of-charge voltage of at least 4.0 volts, more preferably of at least4.4 volts, more preferably of at least 4.8 volts, more preferably of atleast 5.2 volts, more preferably of at least 5.6 volts and mostpreferably of at least 6.0 volts.

The service life of the rechargeable battery cell comprising thiselectrolyte is significantly longer than that of rechargeable batterycells comprising electrolytes known from the prior art.

Furthermore, a rechargeable battery cell having such an electrolyte isalso resistant to low temperatures. At a temperature of −40° C., forexample, 61% of the charged capacity can still be discharged. Theconductivity of the electrolyte at low temperatures is sufficient tooperate a battery cell.

Furthermore, a rechargeable battery cell having such an electrolyteexhibits increased stability with respect to residual amounts of water.If there are still small residual amounts of water in the electrolyte(in the range of ppm), the electrolyte or the first conducting saltforms hydrolysis products with the water, which products, compared tothe SO₂-based electrolytes known from the prior art, are significantlyless aggressive towards the cell components. Because of this, theabsence of water in the electrolyte plays a less important role inSO₂-based electrolytes in comparison to those known from the prior art.These advantages of the electrolyte according to this disclosureoutweigh the disadvantage that arises from the fact that the firstconducting salt according to formula (I) has a significantly largeranion size than the conducting salts known from the prior art. Thishigher anion size leads to a lower conductivity of the first conductingsalt according to formula (I) compared to the conductivity of LiAlCl₄.

Positive Electrode

Advantageous developments of the rechargeable battery cell according tothis disclosure with regard to the positive electrode are describedbelow.

The positive electrode comprises at least one compound in the form of alayered oxide as an active material. Said active material can store ionsof the active metal and release and take up the ions of the active metalduring operation of the battery cell.

In a first advantageous development of the rechargeable battery cellaccording to this disclosure, the compound has the compositionA_(x)M′_(y)M″_(z)O_(a). In this composition, A_(x)M′_(y)M″_(z)O_(a)

-   -   A is at least one metal selected from the group formed by the        alkali metals, the alkaline earth metals, the metals of group 12        of the periodic table or aluminum,    -   M′ is at least one metal selected from the group formed by the        elements Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn;    -   M″ is at least one element selected from the group formed by the        elements of groups 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,        15 and 16 of the periodic table of the elements;    -   x and y independently of one another are numbers greater than 0;    -   z is a number greater than or equal to 0; and    -   a is a number greater than 0.

A is preferably the metal lithium, that is, the compound can have thecomposition Li_(x)M′_(y)M″_(z)O_(a).

These layered oxides are oxides derived from the α-NaFeO₂ structuretype. The oxygen atoms occupy the lattice sites of a face-centered cubiclattice (so-called fcc lattice); the metal ions A and the metal cationsM′ and M″ occupy the existing octahedral holes. In the structureconstructed in this way, there is an order/separation of lithium and thetransition metals on alternating layers along the cubic [111] direction.If an excess of metal ions A is used, these can be integrated into thelayer of metal cations M′ and M″.

The indices y and z in the composition A_(x)M′_(y)M″_(z)O_(a) relate tothe totality of metals and elements that are represented by M′ and M″,respectively. If, for example, M′ comprises two metals M′¹ and M′², thefollowing applies to the index y: y=y1+y2, wherein y1 and y2 representthe indices of the metals M′¹ and M′². The numbers or indices x, y, zand a must be chosen such that there is charge neutrality within thecomposition.

Examples of compounds in which M′ comprises two metals are lithiumnickel manganese cobalt oxides of the compositionLi_(x)Ni_(y1)Mn_(y2)Co_(z)O₂ with M′¹=Ni, M′²=Mn and M″=Co. Examples ofcompounds in which z=0, that is, which have no further metal or elementM″, are lithium cobalt oxides Li_(x)Co_(y)O_(a).

An advantageous development of the rechargeable battery cell accordingto this disclosure provides that A is lithium and M′ is cobalt, whereinx and y are preferably equal to 1, z is equal to 0 and a is preferablyequal to 2. These are preferably compositions of the formulaLi_(x)Co_(y)O_(a), that is, lithium cobalt oxides. The compound LiCoO₂is an example of a lithium cobalt oxide.

A further advantageous development of the rechargeable battery cellaccording to this disclosure provides that M′ consists of the metalsnickel and manganese and M″ is cobalt. In this composition of theformula Li_(x)Ni_(y1)Mn_(y2)Co_(z)O_(a), x, y1 and y2 are, independentlyof one another, numbers greater than 0, z is a number greater than orequal to 0, and a is a number greater than 0. These can be compositionsof the formula Li_(x)Ni_(y1)Mn_(y2)Co_(z)O₂ (NMC), that is, lithiumnickel manganese cobalt oxide. Examples of these lithium nickelmanganese cobalt oxide active materials are LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂(NMC111), LiNi_(0.6)Mn_(0.2)Co_(0.2)O₂ (NMC622) andLiNi_(0.8)Mn_(0.1)Co_(0.1)O₂ (NMC811). Further compounds of lithiumnickel manganese cobalt oxide can have the compositionLiNi_(0.5)Mn_(0.3)Co_(0.2)O₂, LiNi_(0.5)Mn_(0.25)Co_(0.25)O₂,LiNi_(0.52)Mn_(0.32)Co_(0.16)O₂, LiNi_(0.55)Mn_(0.30)Co_(0.15)O₂,LiNi_(0.58)Mn_(0.14)Co_(0.28)O₂, LiNi_(0.64)Mn_(0.18)Co_(0.18)O₂,LiNi_(0.65)Mn_(0.27)Co_(0.08)O₂, LiNi_(0.7)Mn_(0.2)Co_(0.01)O₂,LiNi_(0.7)Mn_(0.15)Co_(0.15)O₂, LiNi_(0.72)Mn_(0.10)Co_(0.18)O₂,LiNi_(0.76)Mn_(0.14)Co_(0.10)O₂, LiNi_(0.86)Mn_(0.04)Co_(0.10)O₂,LiNi_(0.90)Mn_(0.05)Co_(0.05)O₂, LiNi_(0.95)Mn_(0.025)Co_(0.025)O₂ or acombination thereof. Electrodes for rechargeable battery cells having acell voltage of, for example, over 4.6 volts can be produced using thesecompounds.

A further advantageous development of the rechargeable battery cellaccording to this disclosure provides that the active material is ametal oxide which is rich in lithium and manganese (lithium andmanganese-rich oxide material). These materials can be described withthe following formulas: Li_(x)Mn_(y)M″_(z)O_(a). M′ of the formulaLi_(x)M′_(y)M″_(z)O_(a) described above thus represents the metalmanganese (Mn). M″ is, as defined above, at least one element selectedfrom the group formed by the elements of groups 2, 3, 4, 5, 6, 7, 8, 9,10, 11, 12, 13, 14, 15 and 16 of the periodic table of the elements. Theindex x here is greater than or equal to 1, the index y is greater thanthe index z or greater than the sum of the indices z1+z2+z3 etc. Forexample, if M″ comprises two metals M″¹ and M″² with the indices z1 andz2 (for example, Li_(1.2)Mn_(0.525)Ni_(0.175)Co_(0.1)O₂ with M″¹=Niz1=0.175 and M″²=Co z2=0.1), the following applies for the index y:y>z1+z2, The index z is greater than or equal to 0 and the index a isgreater than 0. The indices x, y, z and a must be chosen such that thereis charge neutrality within the composition. Metal oxides which are richin lithium and manganese can also be described by the formula:

-   -   mLi₂MnO₃.(1−m)LiM′O₂ with 0<m<1. Examples of such compounds are        Li_(1.2)Mn_(0.525)Ni_(0.175)Co_(0.1)O₂,Li_(1.2)Mn_(0.6)Ni_(0.2)O₂,Li_(1.2)Ni_(0.13)Co_(0.13)Mn_(0.54)O₂        or Li_(1.16)Mn_(0.61)Ni_(0.15)Co_(0.16)O₂.

It is within the scope of this disclosure for the positive electrode tocomprise at least one of the described layered oxide compounds or acombination of the layered oxide compounds as the active material. Acombination of the layered oxide compounds refers to a positiveelectrode which comprises at least two of the materials described.

It is also within the scope of this disclosure for the positiveelectrode to also comprise, as an active material, a combination of atleast one of the layered oxide compounds described above and at leastone further compound which is not a layered oxide compound. Thecombination can also comprise a plurality of the layered oxide compoundsdescribed above and/or a plurality of further compounds that are notlayered oxide compounds. Said further compound can, for example, be apolyanionic compound, such as lithium manganese iron phosphate.

A further advantageous development of the battery cell according to thisdisclosure provides that the positive electrode has a discharge element.This means that the positive electrode also comprises a dischargeelement in addition to the active material. Said discharge elementserves to enable the required electronically conductive connection ofthe active material of the positive electrode. For this purpose, thedischarge element is in contact with the active material involved in theelectrode reaction of the positive electrode.

Said discharge element can be designed in a planar manner in the form ofa thin metal sheet or a thin metal foil. The thin metal foil preferablyhas a perforated or mesh-like structure. The planar discharge elementcan also consist of a plastic film coated with metal. Said metalcoatings have a thickness in the range from 0.1 μm to 20 μm. The activematerial of the positive electrode is preferably applied to the surfaceof the thin metal sheet, the thin metal foil or the metal-coated plasticfoil. The active material can be applied to the front and/or the rearside of the planar discharge element. Such planar discharge elementshave a thickness in the range from 5 μm to 50 μm. A thickness of theplanar discharge element in the range from 10 μm to 30 μm is preferred.When using planar discharge elements, the positive electrode can have atotal thickness of at least 20 μm, preferably at least 40 μm andparticularly preferably at least 60 μm. The maximum thickness is at most200 μm, preferably at most 150 μm and particularly preferably at most100 μm. The area-specific capacity of the positive electrode based onthe coating on one side is preferably at least 0.5 mAh/cm² when using aplanar discharge element, wherein the following values are furtherpreferred in this order: 1 mAh/cm², 3 mAh/cm², 5 mAh/cm², 10 mAh/cm², 15mAh/cm², 20 mAh/cm².

Furthermore, there is also the possibility for the discharge element ofthe positive electrode to be designed three-dimensionally in the form ofa porous metal structure, in particular in the form of a metal foam. Thethree-dimensional porous metal structure is sufficiently porous suchthat the active material of the positive electrode can be incorporatedinto the pores of the metal structure. The amount of active materialincorporated or applied is the loading on the positive electrode. Whenthe discharge element is designed three-dimensionally in the form of aporous metal structure, in particular in the form of a metal foam, thenthe positive electrode preferably has a thickness of at least 0.2 mm,more preferably at least 0.3 mm, more preferably at least 0.4 mm, morepreferably at least 0.5 mm and most preferably at least 0.6 mm. Afurther advantageous embodiment provides that the area-specific capacityof the positive electrode when using a three-dimensional dischargeelement, in particular in the form of a metal foam, is preferably atleast 2.5 mAh/cm², wherein the following values are further preferred inthis order: 5 mAh/cm², 15 mAh/cm², 25 mAh/cm², 35 mAh/cm², 45 mAh/cm²,55 mAh/cm², 65 mAh/cm², 75 mAh/cm². When the discharge element isdesigned three-dimensionally in the form of a porous metal structure, inparticular in the form of a metal foam, the amount of active material ofthe positive electrode, that is, the loading of the electrode, based onits area, is at least 10 mg/cm², preferably at least 20 mg/cm², morepreferably at least 40 mg/cm², more preferably at least 60 mg/cm², morepreferably at least 80 mg/cm² and most preferably at least 100 mg/cm².This loading of the positive electrode has a positive effect on thecharging process and the discharging process of the rechargeable batterycell.

In a further advantageous development of the battery cell according tothis disclosure, the positive electrode has at least one binder. Saidbinder is preferably a fluorinated binder, in particular apolyvinylidene fluoride and/or a terpolymer which is formed fromtetrafluoroethylene, hexafluoropropylene and vinylidene fluoride.However, it can also be a binder which consists of a polymer which iscomposed of monomeric structural units of a conjugated carboxylic acidor of the alkali, alkaline earth or ammonium salt of this conjugatedcarboxylic acid or of a combination thereof. Furthermore, the binder canalso consist of a polymer based on monomeric styrene and butadienestructural units. In addition, the binder can also be a binder from thegroup of carboxymethyl celluloses. The binder is present in the positiveelectrode, preferably in a concentration of at most 20% by weight, morepreferably at most 15% by weight, more preferably at most 10% by weight,more preferably at most 7% by weight, more preferably at most 5% byweight and most preferably at most 2% by weight based on the totalweight of the positive electrode.

Electrolyte

Advantageous developments of the rechargeable battery cell with regardto the SO₂-based electrolyte are described below.

In a further advantageous embodiment of the rechargeable battery cells,the substituents R¹, R², R³ and R⁴ of the first conducting salt areselected independently of one another from the group formed by:

-   -   C₁-C₆ alkyl; preferably from C₂-C₄ alkyl; particularly        preferably from the alkyl groups 2-propyl, methyl and ethyl;    -   C₂-C₆ alkenyl; preferably from C₂-C₄ alkenyl; particularly        preferably from the alkenyl groups ethenyl and propenyl;    -   C₂-C₆ alkynyl; preferably from C₂-C₄ alkynyl;    -   C₃-C₆ cycloalkyl;    -   phenyl; and    -   C₅-C₇ heteroaryl.

In the case of this advantageous embodiment of the SO₂-basedelectrolyte, the term “C₁-C₆ alkyl” includes linear or branchedsaturated hydrocarbon groups having one to six hydrocarbon groups, inparticular methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl,iso-butyl, tert-butyl, n-pentyl, iso-pentyl, 2,2-dimethylpropyl, n-hexyland iso-hexyl. C₂-C₄ alkyls are preferred among these. The C₂-C₄ alkyls2-propyl, methyl and ethyl are particularly preferred.

In the case of this advantageous embodiment of the SO₂-basedelectrolyte, the term “C₂-C₆ alkenyl” includes unsaturated linear orbranched hydrocarbon groups having two to six carbon atoms, wherein thehydrocarbon groups have at least one C—C double bond. These include inparticular ethenyl, 1-propenyl, 2-propenyl, 1-n-butenyl, 2-n-butenyl,isobutenyl, 1-pentenyl and 1-hexenyl, wherein C₂-C₄ alkenyls arepreferred. Ethenyl and 1-propenyl are particularly preferred.

In the case of this advantageous embodiment of the SO₂-basedelectrolyte, the term “C₂-C₆ alkynyl” includes unsaturated linear orbranched hydrocarbon groups having two to six carbon atoms, wherein thehydrocarbon groups have at least one C—C triple bond. These include inparticular ethynyl, 1-propynyl, 2-propynyl, 1-n-butynyl, 2-n-butynyl,iso-butynyl, 1-pentynyl and 1-hexynyl. Preferred among these are C₂-C₄alkynyls.

In the case of this advantageous embodiment of the SO₂-basedelectrolyte, the term “C₃-C₆ cycloalkyl” includes cyclic saturatedhydrocarbon groups having three to six carbon atoms. These include inparticular cyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl.

In the case of this advantageous embodiment of the SO₂-basedelectrolyte, the term “C₅-C₇ heteroaryl” includes phenyl and naphthyl.

To improve the solubility of the first conducting salt in the SO₂-basedelectrolytes, the substituents R¹, R², R³ and R⁴ are substituted, in afurther advantageous embodiment of the rechargeable battery cell, by atleast one fluorine atom and/or by at least one chemical group, whereinthe chemical group is selected from the group formed by C₁-C₄ alkyl,C₂-C₄ alkenyl, C₂-C₄ alkynyl, phenyl and benzyl. The chemical groupsC₁-C₄ alkyl, C₂-C₄ alkenyl, C₂-C₄ alkynyl, phenyl and benzyl have thesame properties or chemical structures as the hydrocarbon groupsdescribed above. Substituted in this context means that individual atomsor groups of atoms of the substituents R¹, R², R³ and R⁴ have beenreplaced by the fluorine atom and/or by the chemical group.

A particularly high solubility of the first conducting salt in theSO₂-based electrolytes can be achieved by at least one of thesubstituents R¹, R², R³ and R⁴ being a CF₃ group or an OSO₂CF₃ group.

In a further advantageous development of the rechargeable battery cell,the first conducting salt is selected from the group formed by:

In order to adjust the conductivity and/or other properties of theelectrolyte to a desired value, the electrolyte in a furtheradvantageous embodiment of the rechargeable battery cell according tothis disclosure has at least one second conducting salt different fromthe first conducting salt according to formula (I). This means that, inaddition to the first conducting salt, the electrolyte can comprise a oreven further second conducting salts which differ from the firstconducting salt in their chemical composition and their chemicalstructure.

In a further advantageous embodiment of the rechargeable battery cellaccording to this disclosure, the second conducting salt is an alkalimetal compound, in particular a lithium compound. The alkali metalcompound or the lithium compound are selected from the group formed byan aluminate, a halide, an oxalate, a borate, a phosphate, an arsenateand a gallate. The second conducting salt is preferably a lithiumtetrahaloaluminate, in particular LiAlCl₄.

Furthermore, in a further advantageous embodiment of the rechargeablebattery cell according to this disclosure, the electrolyte comprises atleast one additive. This additive is preferably selected from the groupformed by vinylene carbonate and its derivatives, vinylethylenecarbonate and its derivatives, methylethylene carbonate and itsderivatives, lithium (bisoxalato)borate, lithiumdifluoro(oxalato)borate, lithium tetrafluoro(oxalato)phosphate, lithiumoxalate, 2-vinylpyridine, 4-vinylpyridine, cyclic exomethylenecarbonates, sultones, cyclic and acyclic sulfonates, acyclic sulfites,cyclic and acyclic sulfinates, organic esters of inorganic acids,acyclic and cyclic alkanes, which acyclic and cyclic alkanes have aboiling point of at least 36° C. at 1 bar, aromatic compounds,halogenated cyclic and acyclic sulfonylimides, halogenated cyclic andacyclic phosphate esters, halogenated cyclic and acyclic phosphines,halogenated cyclic and acyclic phosphites, halogenated cyclic andacyclic phosphazenes, halogenated cyclic and acyclic silylamines,halogenated cyclic and acyclic halogenated esters, halogenated cyclicand acyclic amides, halogenated cyclic and acyclic anhydrides andhalogenated organic heterocycles.

In relation to the total weight of the electrolyte composition, theelectrolyte has the following composition in a further advantageousdevelopment of the rechargeable battery cell:

-   -   (i) 5 to 99.4% by weight sulfur dioxide,    -   (ii) 0.6 to 95% by weight of the first conducting salt,    -   (iii) 0 to 25% by weight of the second conducting salt and    -   (iv) 0 to 10% by weight of the additive.

As already mentioned above, the electrolyte can comprise not only afirst conducting salt according to formula (I) and a second conductingsalt, but also a plurality of first conducting salts according toformula (I) and a plurality of second conducting salts. In thelast-mentioned case, the aforementioned percentages also include aplurality of first conducting salts and a plurality of second conductingsalts. The molar concentration of the first conducting salt lies in therange from 0.01 mol/L to 10 mol/L, preferably from 0.05 mol/L to 10mol/L, more preferably from 0.1 mol/L to 6 mol/L and most preferablyfrom 0.2 mol/L to 3.5 mol/L, based on the total volume of theelectrolyte.

A further advantageous development of the rechargeable battery cellaccording to this disclosure provides that the electrolyte comprises atleast 0.1 mol SO₂, preferably at least 1 mol SO₂, more preferably atleast 5 mol SO₂, more preferably at least 10 mol SO₂ and most preferablyat least 20 mol SO₂ per mole of conducting salt. The electrolyte canalso comprise very high molar proportions of SO₂, wherein the preferredupper limit value is 2600 mol SO₂ per mole of conducting salt and upperlimits of 1500, 1000, 500 and 100 mol of SO₂ per mole of conducting saltare further preferred in this order. The term “per mole of conductingsalt” refers to all conducting salts that are comprised in theelectrolyte. Electrolytes based on SO₂ having such a concentration ratiobetween SO₂ and the conducting salt have the advantage in that they candissolve a larger amount of conducting salt compared to the electrolytesknown from the prior art, which are based, for example, on an organicsolvent blend. In the context of this disclosure, it was found that,surprisingly, an electrolyte having a relatively low concentration ofconducting salt is advantageous despite the associated higher vaporpressure, in particular with regard to its stability over many chargeand discharge cycles of the rechargeable battery cell. The concentrationof SO₂ in the electrolyte affects its conductivity. Thus, by choosingthe SO₂ concentration, the conductivity of the electrolyte can beadjusted to the planned use of a rechargeable battery cell operatedusing this electrolyte.

The total content of SO₂ and the first conducting salt can be greaterthan 50 percent by weight (% by weight) of the weight of theelectrolyte, preferably greater than 60% by weight, more preferablygreater than 70% by weight, more preferably greater than 80% by weight,more preferably greater than 85% by weight, more preferably greater than90% by weight, more preferably greater than 95% by weight or mostpreferably greater than 99% by weight.

The electrolyte can comprise at least 5% by weight SO₂ based on thetotal amount of the electrolyte comprised in the rechargeable batterycell, wherein values of 20% by weight SO₂, 40% by weight SO₂ and 60% byweight SO₂ are more preferred. The electrolyte can also comprise up to95% by weight SO₂, wherein maximum values of 80% by weight SO₂ and 90%by weight SO₂ are preferred in this order.

It is within the scope of this disclosure for the electrolyte topreferably have only a small percentage or even no percentage of atleast one organic solvent. The proportion of organic solvents in theelectrolyte, which is present, for example, in the form of one solventor a blend of a plurality of solvents, can preferably be at most 50% byweight of the weight of the electrolyte. Lower proportions of at most40% by weight, at most 30% by weight, at most 20% by weight, at most 15%by weight, at most 10% by weight, at most 5% by weight or at most 1% byweight of the electrolyte weight are particularly preferred. Morepreferably, the electrolyte is free of organic solvents. Due to the lowproportion of organic solvents or even their complete absence, theelectrolyte is either hardly combustible or not at all combustible. Thisincreases the operational safety of a rechargeable battery cell operatedusing such an SO₂-based electrolyte. The SO₂-based electrolyte isparticularly preferably essentially free of organic solvents.

In relation to the total weight of the electrolyte composition, theelectrolyte has the following composition in a further advantageousdevelopment of the rechargeable battery cell:

-   -   (i) 5 to 99.4% by weight sulfur dioxide,    -   (ii) 0.6 to 95% by weight of the first conducting salt,    -   (iii) 0 to 25% by weight of the second conducting salt,    -   (iv) 0 to 10% by weight of the additive and    -   (v) 0 to 50% by weight of an organic solvent.

Active Metal

Advantageous developments of the rechargeable battery cell according tothis disclosure with regard to the active metal are described below.

In a first advantageous development of the rechargeable battery cell,the active metal is:

-   -   an alkali metal, in particular lithium or sodium;    -   an alkaline earth metal, in particular calcium;    -   a metal from group 12 of the periodic table, in particular zinc;        or    -   aluminum.

Negative Electrode

Advantageous developments of the rechargeable battery cell according tothis disclosure with regard to the negative electrode are describedbelow.

A further advantageous development of the battery cell according to thisdisclosure provides that the negative electrode is an insertion element.Said insertion electrode comprises an insertion material as the activematerial, in which the ions of the active metal can be stored during thecharging of the rechargeable battery cell and from which the ions of theactive metal can be removed during the discharging of the rechargeablebattery cell. This means that the electrode processes can take place notonly on the surface of the electrode, but also in the interior of thenegative electrode. If, for example, a conducting salt based on lithiumis used, then lithium ions can be stored in the insertion material whilethe rechargeable battery cell is being charged and can be removedtherefrom while the rechargeable battery cell is being discharged. Thenegative electrode preferably comprises carbon as an active material orinsertion material, in particular carbon in the allotrope graphite.However, it is also within the scope of this disclosure for the carbonto be present in the form of natural graphite (flake conveyor orrounded), synthetic graphite (mesophase graphite), graphitizedmesocarbon microbeads (MCMB), with carbon-coated graphite or amorphouscarbon.

In a further advantageous development of the rechargeable battery cellaccording to this disclosure, the negative electrode comprises lithiumintercalation anode active materials that do not comprise carbon, suchas lithium titanates (for example, Li₄Ti₅O₁₂).

A further advantageous development of the rechargeable battery cellaccording to this disclosure provides that the negative electrodecomprises anode active materials which form an alloy with lithium. Theseare, for example, lithium-storing metals and metal alloys (for example,Si, Ge, Sn, SnCo_(x)C_(y), SnSi_(x) and the like) and oxides oflithium-storing metals and metal alloys (for example, SnO_(x), SiO_(x),oxidic glasses of Sn, Si and the like).

In a further advantageous development of the rechargeable battery cellaccording to this disclosure, the negative electrode comprisesconversion anode active materials. Said conversion anode activematerials can be, for example, transition metal oxides in the form ofmanganese oxides (MnO_(x)), iron oxides (FeO_(x)), cobalt oxides(CoO_(x)), nickel oxides (NiO_(x)), copper oxides (CuO_(x)) or metalhydrides in the form of magnesium hydride (MgH₂), titanium hydride(TiH₂), aluminum hydride (AlH₃) and boron, aluminum and magnesium basedternary hydrides and the like.

In a further advantageous development of the rechargeable battery cellaccording to this disclosure, the negative electrode comprises a metal,in particular metallic lithium.

A further advantageous development of the rechargeable battery cellaccording to this disclosure provides that the negative electrode isporous, wherein the porosity is preferably at most 50%, more preferablyat most 45%, more preferably at most 40%, more preferably at most 35%,more preferably at most 30%, more preferably at most 20% and mostpreferably at most 10%. The porosity represents the cavity volume inrelation to the total volume of the negative electrode, wherein thecavity volume is formed by so-called pores or cavities. This porosityleads to an increase in the inner surface area of the negativeelectrode. Furthermore, the porosity reduces the density of the negativeelectrode and thus also its weight. The individual pores of the negativeelectrode can preferably be completely filled with the electrolyteduring operation.

A further advantageous development of the battery cell according to thisdisclosure provides that the negative electrode has a discharge element.This means that in addition to the active material or insertionmaterial, the negative electrode also comprises a discharge element.This discharge element serves to enable the required electronicallyconductive connection of the active material of the negative electrode.For this purpose, the discharge element is in contact with the activematerial involved in the electrode reaction of the negative electrode.Said discharge element can be designed in a planar manner in the form ofa thin metal sheet or a thin metal foil. The thin metal foil preferablyhas a perforated or mesh-like structure. The planar discharge elementcan also consist of a plastic film coated with metal. Said metalcoatings have a thickness in the range from 0.1 μm to 20 μm. The activematerial of the negative electrode is preferably applied to the surfaceof the thin metal sheet, the thin metal foil or the metal-coated plasticfoil. The active material can be applied to the front and/or the rearside of the planar discharge element. Such planar discharge elementshave a thickness in the range from 5 μm to 50 μm. A thickness of theplanar discharge element in the range from 10 μm to 30 μm is preferred.When using planar discharge elements, the negative electrode can have atotal thickness of at least 20 μm, preferably at least 40 μm andparticularly preferably at least 60 μm. The maximum thickness is at most200 μm, preferably at most 150 μm and particularly preferably at most100 μm. The area-specific capacity of the negative electrode based onthe coating on one side is preferably at least 0.5 mAh/cm² when using aplanar discharge element, wherein the following values are furtherpreferred in this order: 1 mAh/cm², 3 mAh/cm², 5 mAh/cm², 10 mAh/cm², 15mAh/cm², 20 mAh/cm².

Furthermore, there is also the possibility for the discharge element tobe designed three-dimensionally in the form of a porous metal structure,in particular in the form of a metal foam. The term “three-dimensionalporous metal structure” refers to any structure consisting of metal thatnot only extends over the length and width of the flat electrode likethe thin metal sheet or the metal foil, but also over its thicknessdimension. The three-dimensional porous metal structure is sufficientlyporous such that the active material of the negative electrode can beincorporated into the pores of the metal structure. The amount of activematerial incorporated or applied is the loading on the negativeelectrode. When the discharge element is designed three-dimensionally inthe form of a porous metal structure, in particular in the form of ametal foam, then the negative electrode preferably has a thickness of atleast 0.2 mm, more preferably at least 0.3 mm, more preferably at least0.4 mm, more preferably at least 0.5 mm and most preferably at least 0.6mm. In this case, the thickness of the electrodes is significantlygreater compared to negative electrodes, which is the case with organiclithium-ion cells. A further advantageous embodiment provides that thearea-specific capacity of the negative electrode when using athree-dimensional discharge element, in particular in the form of ametal foam, is preferably at least 2.5 mAh/cm², wherein the followingvalues are further preferred in this order: 5 mAh/cm², 15 mAh/cm², 25mAh/cm², 35 mAh/cm², 45 mAh/cm², 55 mAh/cm², 65 mAh/cm², 75 mAh/cm².When the discharge element is designed three-dimensionally in the formof a porous metal structure, in particular in the form of a metal foam,the amount of active material of the negative electrode, that is, theloading of the electrode, based on its area, is at least 10 mg/cm²,preferably at least 20 mg/cm², more preferably at least 40 mg/cm², morepreferably at least 60 mg/cm², more preferably at least 80 mg/cm² andmost preferably at least 100 mg/cm². This loading of the negativeelectrode has a positive effect on the charging process and thedischarging process of the rechargeable battery cell.

In a further advantageous development of the battery cell according tothis disclosure, the negative electrode has at least one binder. Saidbinder is preferably a fluorinated binder, in particular apolyvinylidene fluoride and/or a terpolymer which is formed fromtetrafluoroethylene, hexafluoropropylene and vinylidene fluoride.However, it can also be a binder which consists of a polymer which iscomposed of monomeric structural units of a conjugated carboxylic acidor of the alkali, alkaline earth or ammonium salt of this conjugatedcarboxylic acid or of a combination thereof. Furthermore, the binder canalso consist of a polymer based on monomeric styrene and butadienestructural units. In addition, the binder can also be a binder from thegroup of carboxymethyl celluloses. The binder is present in the negativeelectrode, preferably in a concentration of at most 20% by weight, morepreferably at most 15% by weight, more preferably at most 10% by weight,more preferably at most 7% by weight, more preferably at most 5% byweight and most preferably at most 2% by weight based on the totalweight of the negative electrode.

In a further advantageous development of the battery cell according tothis disclosure, the negative electrode has at least one conductivityadditive. The conductivity additive should preferably have a low weight,high chemical resistance and a high specific surface area, examples ofconductivity additives are particulate carbon (carbon black, Super P,acetylen black), fibrous carbon (carbon nanotubes CNT, carbon(nano)fibers), finely divided graphites and graphene (nanosheets).

Structure of the Rechargeable Battery Cell

Advantageous developments of the rechargeable battery cell according tothis disclosure are described below with regard to their structure.

In order to further improve the function of the rechargeable batterycell, a further advantageous development of the rechargeable batterycell according to this disclosure provides that the rechargeable batterycell comprises a plurality of negative electrodes and a plurality ofpositive electrodes, which are stacked alternately in the housing. Here,the positive electrodes and the negative electrodes are preferably eachelectrically separated from one another by separators.

The separator can be formed from a non-woven material, a membrane, awoven material, a knitted material, an organic material, an inorganicmaterial or a combination thereof. Organic separators can consist ofunsubstituted polyolefins (for example, polypropylene or polyethylene),partially to completely halogen-substituted polyolefins (for example,partially to completely fluorine-substituted, in particular PVDF, ETFE,PTFE), polyesters, polyamides or polysulfones. Separators that comprisea combination of organic and inorganic materials are, for example, glassfiber textile materials in which the glass fibers are provided with asuitable polymer coating. The coating preferably comprises afluorine-containing polymer such as polytetrafluoroethylene (PTFE),ethylene-tetrafluoroethylene (ETFE), perfluoroethylene propylene (FEP),THV (terpolymer of tetrafluoroethylene, hexafluoroethylene andvinylidene fluoride), a perfluoroalkoxy polymer (PFA), aminosilane,polypropylene or polyethylene (PE). The separator can also be folded inthe housing of the rechargeable battery cell, for example, in the formof so-called “Z-folding.” In this Z-folding, a strip-shaped separator isfolded in a Z-like manner through or around the electrodes. Furthermore,the separator can also be formed as separator paper.

It is also within the scope of this disclosure for the separator to beable to be designed as a sheath, wherein each positive electrode or eachnegative electrode is enveloped by the sheath. The sheath can be formedfrom a non-woven material, a membrane, a woven material, a knittedmaterial, an organic material, an inorganic material or a combinationthereof.

A sheath on the positive electrode leads to more uniform ion migrationand ion distribution in the rechargeable battery cell. The more even theion distribution, in particular in the negative electrode, the higherthe possible loading of the negative electrode with active material and,as a result, the usable capacity of the rechargeable battery cell. Atthe same time, risks are avoided that could be associated with unevenloading and the resulting deposition of the active metal. Theseadvantages are particularly effective when the positive electrodes ofthe rechargeable battery cell are enveloped in the sheath.

The surface dimensions of the electrodes and the sheath can preferablybe matched to one another such that the external dimensions of thesheath of the electrodes and the external dimensions of the unsheathedelectrodes match at least in one dimension.

The surface area of the sheath can preferably be greater than thesurface area of the electrode. In this case, the sheath extends beyond aboundary of the electrode. Two layers of the sheath covering theelectrode on both sides can therefore be connected to one another at theedge of the positive electrode by an edge connection.

In a further advantageous embodiment of the rechargeable battery cellaccording to this disclosure, the negative electrodes have a sheath,while the positive electrodes have no sheath.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned aspects of exemplary embodiments will become moreapparent and will be better understood by reference to the followingdescription of the embodiments taken in conjunction with theaccompanying drawings, wherein:

FIG. 1 shows a first embodiment of a rechargeable battery cell accordingto this disclosure in a cross-sectional illustration;

FIG. 2 shows an electron microscope image of the three-dimensionalporous structure of the metal foam of the first embodiment from FIG. 1as a detailed illustration;

FIG. 3 shows a second embodiment of a rechargeable battery cellaccording to this disclosure in a cross-sectional illustration;

FIG. 4 shows a detail of the second embodiment from FIG. 3;

FIG. 5 shows a third embodiment of the rechargeable battery cellaccording to this disclosure in an exploded illustration;

FIG. 6 shows the discharge capacity as a function of the number ofcycles of test full cells, which comprise lithium nickel manganesecobalt oxide (NMC) of the composition LiNi_(0.6)Mn_(0.2)Co_(0.2)O₂(NMC622) and LiNi_(0.8)Mn_(0.1)Co_(0.2)O₂ (NMC811) as the activematerial of the positive electrode;

FIG. 7 shows the discharge capacity as a function of the number ofcycles of test full cells that comprise lithium cobalt oxide LiCoO₂(LCO) as the active material of the positive electrode, wherein areference test full cell is filled with the reference electrolyte and atest full cell is filled with electrolyte 1 from Example 2;

FIG. 8 shows the discharge capacity as a function of the number ofcycles of test full cells comprising lithium nickel manganese cobaltoxide (NMC) of the composition LiNi_(0.6)Mn_(0.2)Co_(0.2)O₂ (NMC622) asthe active material of the positive electrode, wherein a reference testfull cell is filled with the reference electrolyte and a full test cellis filled with electrolyte 1 from Example 2;

FIG. 9 shows the discharge capacity as a function of the number ofcycles of a test full cell having a metal oxide of the compositionLi_(1.16)Mn_(0.61)Ni_(0.15)Co_(0.16)O₂ as the active material of thepositive electrode, wherein the end-of-charge voltage is 4.8 volts;

FIG. 10 shows the potential profile in volts [V] as a function of thepercentage charge of cycle 1 and cycle 2 of a test full cell having ametal oxide of the composition Li_(1.16)Mn_(0.61)Ni_(0.15)Co_(0.16)O₂ asthe active material of the positive electrode;

FIG. 11 shows the potential in [V] of three test full cells which werefilled with electrolytes 1, 3 and 4 from Example 2 when charging anegative electrode as a function of the capacity, which is related tothe theoretical capacity of the negative electrode, during formation ofa coating layer on the negative electrode;

FIG. 12 shows the potential profile during discharge in volts as afunction of the percentage charge of three test full cells which werefilled with electrolytes 1, 3 and 4 from Example 2 and comprised lithiumnickel manganese cobalt oxide (NMC) as the active electrode material;

FIG. 13 shows the conductivity in [mS/cm] of electrolyte 1 from Example2 as a function of the concentration of compound 1;

FIG. 14 shows the conductivity in [mS/cm] of electrolyte 3 from Example2 as a function of the concentration of compound 3; and

FIG. 15 shows the conductivity in [mS/cm] of electrolyte 4 from Example2 as a function of the concentration of compound 4.

DESCRIPTION

The embodiments described below are not intended to be exhaustive or tolimit the invention to the precise forms disclosed in the followingdetailed description. Rather, the embodiments are chosen and describedso that others skilled in the art may appreciate and understand theprinciples and practices of this disclosure.

FIG. 1 shows a first embodiment of a rechargeable battery cell 2according to this disclosure in a cross-sectional illustration. Saidrechargeable battery cell 2 is designed as a prismatic cell and has ahousing 1, among other things. Said housing 1 encloses an electrodearray 3 which comprises three positive electrodes 4 and four negativeelectrodes 5. The positive electrodes 4 and the negative electrodes 5are stacked alternately in the electrode array 3. The housing 1 can,however, also accommodate more positive electrodes 4 and/or negativeelectrodes 5. In general, it is preferred when the number of negativeelectrodes 5 is one greater than the number of positive electrodes 4.This has the consequence of the outer end faces of the electrode stackbeing formed by the electrode surfaces of the negative electrodes 5. Theelectrodes 4, 5 are connected to corresponding contacts 9, 10 of therechargeable battery cell 2 via electrode connections 6, 7. Therechargeable battery cell 2 is filled with an SO₂-based electrolyte suchthat the electrolyte penetrates as completely as possible into all poresor cavities, in particular within the electrodes 4, 5. The electrolyteis not visible in FIG. 1. In the present embodiment, the positiveelectrodes 4 comprise an intercalation compound as an active material.This intercalation compound is LiCoO₂.

The electrodes 4, 5 are designed flat in the present embodiment, thatis, as layers having a thickness that is smaller in relation to theirsurface area. They are each separated from one another by separators 11.The housing 1 of the rechargeable battery cell 2 is essentially designedas a rectangular parallelepiped, wherein the electrodes 4, 5 and thewalls of the housing 1 shown in a sectional illustration extendperpendicular to the plane of the drawing and are essentially straightand flat. The rechargeable battery cell 2 can, however, also be designedas a winding cell in which the electrodes consist of thin layers thatare wound up together with a separator material. The separators 11, onthe one hand, separate the positive electrode 4 and the negativeelectrode 5 spatially and electrically and, on the other hand, arepermeable to the ions of the active metal, among other things. In thisway, large electrochemically effective surfaces are created, whichenable a correspondingly high current yield.

The electrodes 4, 5 also have a discharge element which serves to enablethe required electronically conductive connection of the active materialof the respective electrode. Said discharge element is in contact withthe active material involved in the electrode reaction of the respectiveelectrode 4, 5 (not depicted in FIG. 1). The discharge element isdesigned in the form of a porous metal foam 18. The metal foam 18extends over the thickness dimension of the electrodes 4, 5. The activematerial of the positive electrodes 4 and the negative electrodes 5 isincorporated into the pores of said metal foam 18, such that it fillsthe pores of the metal foam evenly over the entire thickness of themetal structure. The positive electrodes 4 comprise a binder to improvethe mechanical strength. This binder is a fluoropolymer. The negativeelectrodes 5 comprise carbon as an active material in a form suitable asan insertion material for the absorption of lithium ions. The structureof the negative electrode 5 is similar to that of the positive electrode4.

FIG. 2 shows an electron microscope image of the three-dimensionalporous structure of the metal foam 18 of the first embodiment fromFIG. 1. On the basis of the specified scale, it can be seen that thepores P have an average diameter of more than 100 μm, that is, arerelatively large. This metal foam is a metal foam made of nickel.

FIG. 3 shows a second embodiment of a rechargeable battery cell 20according to this disclosure in a cross-sectional illustration. Saidsecond embodiment differs from the first embodiment shown in FIG. 1 inthat the electrode array comprises a positive electrode 23 and twonegative electrodes 22. They are each separated from one another byseparators 21 and surrounded by a housing 28. The positive electrode 23has a discharge element 26 in the form of a planar metal foil, to whichthe active material 24 of the positive electrode 23 is applied on bothsides. The negative electrodes 22 also comprise a discharge element 27in the form of a planar metal foil, to which the active material 25 ofthe negative electrode 22 is applied on both sides. Alternatively, theplanar discharge elements of the edge electrodes, that is, of theelectrodes that close off the electrode stack, can only be coated withactive material on one side. The non-coated side faces the wall of thehousing 28. The electrodes 22, 23 are connected to correspondingcontacts 31, 32 of the rechargeable battery cell 20 via electrodeconnections 29, 30.

FIG. 4 shows the planar metal foil which serves as a discharge element26, 27 for the positive electrodes 23 and the negative electrodes 22 inthe second embodiment from FIG. 3. This metal foil has a perforated ormesh-like structure having a thickness of 20 μm.

FIG. 5 shows a third embodiment of a rechargeable battery cell 40according to this disclosure in an exploded illustration. This thirdembodiment differs from the two embodiments explained above in that thepositive electrode 44 is enveloped by a sheath 13. In this case, asurface area of the sheath 13 is greater than a surface area of thepositive electrode 44, the boundary 14 of which is shown in FIG. 5 as adashed line. Two layers 15, 16 of the sheath 13 that cover the positiveelectrode 44 on both sides are connected to one another at thecircumferential edge of the positive electrode 44 by an edge connection17. The two negative electrodes 45 are not enveloped. The electrodes 44and 45 can be contacted via the electrode connections 46 and 47.

Example 1: Preparation of a Reference Electrolyte

A reference electrolyte used for the examples described below wasprepared by the method described in patent specification EP 2 954 588B1. First, lithium chloride (LiCl) was dried under vacuum at 120° C. forthree days (hereinafter referred to as [V4]). Aluminum particles (Al)were dried under vacuum for two days at 450° C. LiCl, aluminum chloride(AlCl₃) and Al were mixed together in an AlCl₃:LiCl:Al molar ratio of1:1.06:0.35 in a glass bottle having an opening to allow gas to escape.This blend was thereafter heat-treated in stages to produce a moltensalt. After cooling, the salt melt formed was filtered, then cooled toroom temperature and finally SO₂ was added until the desired molar ratioof SO₂ to LiAlCl₄ was formed. The reference electrolyte thus formed hadthe composition LiAlCl₄*x SO₂, wherein x is dependent on the amount ofSO₂ supplied.

Example 2: Preparation of Four Embodiments 1, 2, 3 and 4 of an SO₂-BasedElectrolyte for a Battery Cell

Four embodiments 1, 2, 3 and 4 of the SO₂-based electrolyte wereprepared for the experiments described below (hereinafter referred to aselectrolytes 1, 2, 3 and 4). For this purpose, four different firstconducting salts according to formula (I) were initially prepared usinga manufacturing process described in the following documents [V5], [V6]and [V7]:

-   [V5] “I. Krossing, Chem. Eur. J. 2001, 7, 490;-   [V6] S. M. Ivanova et al., Chem. Eur. J. 2001, 7, 503;-   [V7] Tsujioka et al., J. Electrochem. Soc., 2004, 151, A1418”

These four different, first conducting salts according to formula (I)are referred to below as compounds 1, 2, 3 and 4. They come from thefamily of polyfluoroalkoxyaluminates and were prepared in hexaneaccording to the following reaction equation, starting from LiAlH₄ andthe corresponding alcohol R—OH with R¹═R²═R³═R⁴.

As a result, compounds 1, 2, 3 and 4 shown below were formed using thesum and structural formulas:

Compounds 1, 2, 3 and 4 were first recrystallized for purification. As aresult, residues of the educt LiAlH₄ were removed from the firstconducting salt, since said educt could possibly lead to the formationof sparks with possibly existing traces of water in SO₂.

Compounds 1, 2, 3 and 4 were then dissolved in SO₂. It was found thatcompounds 1, 2, 3 and 4 dissolve well in SO₂.

The preparation of electrolytes 1, 2, 3 and 4 was performed at lowtemperature or under pressure according to process steps 1 to 4 listedbelow:

-   -   1) receiving of the respective compound 1, 2, 3 and 4 in a        pressure piston each with a riser pipe,    -   2) evacuation of the pressure pistons,    -   3) inflow of liquid SO₂ and    -   4) repetition of steps 2+3 until the target amount of SO₂ was        added.

The respective concentration of compounds 1, 2, 3 and 4 in electrolytes1, 2, 3 and 4 was 0.6 mol/L (molar concentration based on 1 liter of theelectrolyte), unless otherwise described in the description of theexperiment. The experiments described below were performed usingelectrolytes 1, 2, 3 and 4 and the reference electrolyte.

Example 3: Production of Test Full Cells

The test full cells used in the experiments described below arerechargeable battery cells having two negative electrodes and onepositive electrode, each separated by a separator. The positiveelectrodes included an active material, a conductivity mediator and abinder. The negative electrodes comprised graphite as the activematerial and also a binder. As mentioned in the experiment, the negativeelectrodes can also comprise a conductivity additive. The activematerial of the positive electrode is named in the respectiveexperiment. The discharge element of the positive and negativeelectrodes was made of nickel. Among other things, the aim of theinvestigations is to confirm the use of various active materials for thepositive electrode in a battery cell according to this disclosure incombination with the electrolyte according to this disclosure. Table 3shows which active materials were investigated for the positiveelectrode and which upper potentials were used.

TABLE 3 Active Materials Examined Active Upper Experiment MaterialPotential 1 Lithium nickel manganese cobalt oxide (NMC) of 4.4 V thecomposition LiNi_(0.6)Mn_(0.2)Co_(0.2)O₂ (NMC622) 4.6 V andLiNi_(0.8)Mn_(0.1)Co_(0.1)O₂ (NMC811) 5.0 V 2 Lithium cobalt oxideLiCoO₂ (LCO) 4.4 V 3 Lithium nickel manganese cobalt oxide (NMC) of 4.4V the composition LiNi_(0.6)Mn_(0.2)Co_(0.2)O₂ (NMC622) 4Lithium-manganese-rich metal oxide of the 4.8 V compositionLi_(1.16)Mn_(0.61)Ni_(0.15)Co_(0.16)O₂

The test full cells were each filled with the electrolyte required forthe experiments, that is, either with the reference electrolyte orelectrolytes 1, 2, 3 or 4.

Several, that is, two to four, identical test whole cells were producedfor each experiment. The results presented in the experiments are eachmean values from the measured values obtained for the identical testfull cells.

Example 4: Measurement in Test Full Cells

For measurements in test full cells, for example, the discharge capacityis determined from the number of cycles. For this purpose, the test fullcells are charged with a certain charge current intensity up to acertain upper potential. The corresponding upper potential is held untilthe charge current has dropped to a certain value. The discharge thentakes place with a certain discharge current intensity up to a certaindischarge potential. This charging method is a so-called I/U charging.This process is repeated depending on the desired number of cycles. Theupper potentials or the discharge potential and the respective charge ordischarge current intensities are given in the experiments. The value towhich the charge current must have dropped is also described in theexperiments.

The term “upper potential” is used as a synonym for the terms “chargepotential,” “charge voltage,” “end-of-charge voltage” and “upperpotential limit.” The terms denote the voltage/potential up to which acell or battery is charged with the aid of a battery charger.

The battery is preferably charged at a current rate of C/2 and at atemperature of 22° C. With a charge or discharge rate of 1C, bydefinition, the nominal capacity of a test full cell is charged ordischarged in one hour. A charge rate of C/2 means a charge time of 2hours.

The term “discharge potential” is used synonymously with the term “lowercell voltage.” This describes the voltage/potential up to which a cellor battery is discharged with the aid of a battery charger.

The battery is preferably discharged at a current rate of C/2 and at atemperature of 22° C.

The discharge capacity is obtained from the discharge current and thetime until the criteria for ending the discharge are fulfilled. Theassociated figures show mean values for the discharge capacities as afunction of the number of cycles. These mean values of the dischargecapacities are expressed as a percentage of the nominal capacity, oftenstandardized to the maximum capacity that was achieved in the respectivetest. The nominal capacity is obtained by subtracting from thetheoretical capacity of the positive electrode that capacity that isconsumed in the first cycle for the formation of a coating layer on thenegative electrode. This coating layer is formed on the negativeelectrode when the test full cell is charged for the first time. Lithiumions are irreversibly consumed for this formation of a coating layer, sothat the respective test full cell has less cyclic capacity availablefor the subsequent cycles.

Experiment 1: Test Full Cells Having Lithium Nickel Manganese CobaltOxide (NMC) of the Composition LiNi_(0.6)Mn_(0.2)Co_(0.2)O₂ (NMC622) andLiNi_(0.8)Mn_(0.1)Co_(0.1)O₂ (NMC811) as Active Electrode Materials

An experiment was performed in test full cells according to Example 3using positive electrodes made of lithium nickel manganese cobalt oxideof the composition LiNi_(0.6)Mn_(0.2)Co_(0.2)O₂ (NMC622) andLiNi_(0.8)Mn_(0.1)Co_(0.1)O₂ (NMC811) as active electrode materials.Compounds of the composition NMC can be charged in a battery cell havinga suitable electrolyte up to high upper potentials and then dischargedagain. The test full cells were filled with electrolyte 1 described inExample 2. Three test full cells comprised positive electrodes havingthe compound NMC622, and in one test full cell, NMC811 was used as theactive high-voltage cathode material.

To determine the discharge capacities (see Example 4), the test fullcells were charged with a current intensity of 50 mA up to differentupper potentials. The corresponding upper potential was held until thecharge current had dropped to 40 mA. The discharge then took place witha current intensity of 50 mA up to a discharge potential of 2.5 volts.The upper potentials for the three NMC622 test full cells were 4.4volts, 4.6 volts and 5.0 volts. The upper potential of the NMC811 testfull cell was 4.6 volts.

FIG. 6 shows mean values for the discharge capacities of the four testfull cells as a function of the number of cycles. These mean values ofthe discharge capacities are respectively expressed as a percentage ofthe nominal capacity [% nominal capacity]. The profile of the dischargecapacities of the four test full cells shows a uniform, slightlydecreasing profile. The decrease in capacity is somewhat greater inthose test full cells which were cycled at a higher upper potential.Similar experiments using organic lithium-ion cells were performed inthe above-mentioned publication [V1] from the prior art using NMCcathodes and the organic electrolyte LP57, which has the composition 1 MLiPF₆ in EC:EMC 3:7. Table 4 compares the results of Experiment 1 withthose of the experiment from [V1].

The outstanding properties of the battery cells according to thisdisclosure become clear when compared to the prior art. The cathodematerial NMC (622) in battery cells from the prior art shows, in the300th cycle, only a discharge capacity of 94% at an upper potential of4.4 volts and only a discharge capacity of 39% at an upper potential of4.6 volts. In comparison, a cell according to this disclosure having NMC(622) cathode material shows, in the 300th cycle, a discharge capacityof 97% at 4.4 volts, a discharge capacity of 91% at 4.6 volts and even avalue of 84% at a very high upper potential of 5.0 volts.

The cathode material NMC (811) shows a discharge capacity of 66% in the300th cycle at an upper potential of 4.4 volts in the measurements fromthe prior art. The same material still shows a high discharge capacityof 90% in a battery cell according to this disclosure at an upperpotential of 4.6 volts.

TABLE 4 Comparison of the Results of Experiment 1 with the Prior Artfrom Document [V1] Upper Potential: 4.4 V 4.6 V 5.0 V Discharge Capacity[%] Discharge Capacity [%] Discharge Capacity [%] Cycle 300 Cycle 300Cycle 300 Cathode Prior Art Invention Prior Art Invention Prior ArtInvention Material: (Organic Experiment 1 (Organic Experiment 1 (OrganicExperiment 1 Electrolyte; Electrolyte; Electrolyte; 1 M LiPF₆ 1 M LiPF₆1 M LiPF₆ in EC: EMC in EC: EMC in EC: EMC 3:7) 3:7) 3:7) NMC 94% 97%39% 91% — 84% (622) NMC 66% — — 90% — — (811)

Experiment 2: Test Full Cells Having Lithium Cobalt Oxide LiCoO₂ (LCO)as the Active Electrode Material

In a further experiment, two test whole cells were produced according toExample 3. The active material of the positive electrodes (cathodes)consisted of lithium cobalt oxide (LCO).

A first test full cell was filled with a reference electrolyte accordingto Example 1 for this Experiment 2. The electrolyte had the compositionLiAlCl₄*6 SO₂. The two test full cells were filled with electrolyte 1described in Example 2. The test full cells were cycled as described inExperiment 1 to determine the discharge capacities (see Example 4). Theupper potential of the battery cells having reference electrolyte was4.2 volts, that of the cells according to this disclosure was 4.4 volts.

FIG. 7 shows mean values for the discharge capacities of the two testfull cells as a function of the number of cycles. These mean values ofthe discharge capacities are respectively expressed as a percentage ofthe nominal capacity [% nominal capacity]. The profile of the dischargecapacities of the two test full cells shows completely differentbehavior.

The discharge capacity of the test full cell having referenceelectrolyte begins to rise at the 45th cycle and then falls steeply downat the 55th cycle until a capacity of only 50% is reached at cycle 80.Said test full cell is irreversibly damaged. A battery cell thatcomprises a combination of an electrode having lithium cobalt oxide asthe active material and the reference electrolyte is not stable at anupper potential of 4.2 volts.

The cell according to this disclosure shows very stable behavior of thedischarge capacity. A capacity of 97% is still obtained at cycle 200. Abreak had to be made in the measurement between cycle 125 and 126 due todevice maintenance. The capacity after the break was increased by 2%,which is why the profile of the discharge capacity exhibits a localmaximum at this point.

Experiment 3: Test Full Cells Having Lithium Nickel Manganese CobaltOxide (NMC) of the Composition LiNi_(0.6)Mn_(0.2)Co_(0.2)O₂ (NMC622) asthe Active Electrode Material

Experiment 2 was repeated using lithium nickel manganese cobalt oxide(NMC) of the composition LiNi_(0.6)Mn_(0.2)Co_(0.2)O₂ (NMC622) as theactive material of the positive electrodes (cathodes). Two test fullcells were again produced according to Example 3.

A first test full cell was filled with a reference electrolyte accordingto Example 1. The electrolyte had the composition LiAlCl₄*6 SO₂. The twotest full cells were filled with electrolyte 1 described in Example 2.The test full cells were cycled as described in Experiment 1 todetermine the discharge capacities (see Example 4). The upper potentialof the first test full cell having reference electrolyte was 4.2 volts,that of the second test full cell was 4.4 volts.

FIG. 8 shows mean values for the discharge capacities of said two testfull cells as a function of the number of cycles. These mean values ofthe discharge capacities are respectively expressed as a percentage ofthe nominal capacity [% nominal capacity]. Here, too, the profile of thedischarge capacities of the two test full cells shows completelydifferent behavior.

The discharge capacity of the first test full cell having referenceelectrolyte begins to steadily fall from the 75th cycle after previousfluctuations. A capacity of only 86% is reached at cycle 130. The firsttest full cell is irreversibly damaged. A battery cell that comprises acombination of an electrode having lithium nickel manganese cobalt oxide(NMC) of the composition LiNi_(0.6)Mn_(0.2)Co_(0.2)O₂ (NMC622) as theactive material and the reference electrolyte is not stable at an upperpotential of 4.2 volts.

The second test full cell shows very stable behavior of the dischargecapacity. A capacity of 97% is still obtained at cycle 200.

Experiment 4: Test Full Cells Having a Metal Oxide of the CompositionLi_(1.16)Mn_(0.61)Ni_(0.15)Co_(0.16)O₂ as the Active Material of thePositive Electrode

In order to test a metal oxide that is rich in lithium and manganese asthe active electrode material, a test full cell according to Example 3was produced in a further experiment. The active material of thepositive electrodes (cathodes) consisted of a metal oxide of thecomposition Li_(1.16)Mn_(0.61)Ni_(0.15)Co_(0.16)O₂, which is rich inlithium and manganese.

The test full cell was filled with electrolyte 1 described in Example 2.To determine the discharge capacities (see Example 4), the test fullcell was charged with a current intensity of 100 mA up to an upperpotential of 4.8 volts. The corresponding upper potential was held untilthe charge current had dropped to 40 mA. The discharge then took placewith a current intensity of 100 mA up to a discharge potential of 2.0volts.

FIG. 9 shows mean values for the discharge capacities of the test fullcell as a function of the number of cycles. These mean values of thedischarge capacities are respectively expressed as a percentage of thenominal capacity [% nominal capacity]. The test full cell shows verystable behavior of the discharge capacity. A capacity of 90% is stillobtained at cycle 100.

FIG. 10 shows the potential profile in volts [V] of cycle 1 and cycle 2of a test full cell having a metal oxide which is rich in lithium andmanganese. The metal oxide is activated in the first cycle, whichenables the high specific capacities typical of this material.

The potential profile is depicted as a function of the percentage chargethat is related to the maximum charge of the test full cell. The testfull cell was charged at a current of 100 mA up to an upper potential of4.8 V. The potential was held until the charge current had dropped to 40mA. The discharge then took place with a current intensity of 100 mA upto a discharge potential of 2.0 volts.

The potential curve in cycle 1 shows a clearly different behavior thanthe potential curve in cycle 2. This is based on the structural changein the material known in the literature. Irreversible changes to thematerial take place during this process, so that active lithium ions arelost during activation in the first cycle. Only less than 90% of thelithium ions can be stored back in the lattice.

FIG. 10 shows that, in the second cycle, there is a re-storage of morethan 90% and thus the irreversible losses are significantly lower thandescribed in the literature.

In cycle 2, the high potential stability of the electrolyte isparticularly evident insofar as an almost complete intercalation of thelithium ions takes place in cycle 2 at an upper end-of-charge voltage of4.8 V.

Experiment 5: Test Full Cells Having Lithium Nickel Manganese CobaltOxide (NMC) of the Composition LiNi_(0.6)Mn_(0.2)Co_(0.2)O₂ (NMC622) asthe Active Electrode Material in Combination with Electrolyte 1,Electrolyte 3 and Electrolyte 4

Various experiments were performed to investigate electrolytes 1, 3 and4 in combination with lithium nickel manganese cobalt oxide (NMC622) asthe active material of the positive electrode. On the one hand, thecoating layer capacities of electrolytes 1, 3 and 4 were determined and,on the other hand, discharge capacities in all three electrolytes weredetermined.

Three test full cells were filled with electrolytes 1, 3 and 4 describedin Example 2 to determine the coating layer capacity. The three testfull cells comprised lithium nickel manganese cobalt oxide (NMC622) asthe active material of the positive electrode.

FIG. 11 shows the potential in volts of the test full cells whencharging the negative electrode as a function of capacity, which isrelated to the theoretical capacity of the negative electrode. The twocurves depicted show averaged results of several experiments with thetest whole cells described above. First, the test full cells werecharged with a current of 15 mA until a capacity of 125 mAh (Q_(lad))was reached. The test full cells were then discharged at 15 mA until apotential of 2.5 volts was reached. The discharge capacity (Q_(ent)) wasdetermined.

The capacity in % of the theory that was used to form the coating layeron the negative electrode is calculated according to the followingformula:

Coating layer capacity=(Q _(lad)(125 mAh)−Q _(ent)(x mAh))/Q _(NEL)

Q_(NEL) is the theoretical capacity of the negative electrode used. Thetheoretical capacity is calculated, in the case of graphite, to a valueof 372 mAh/g.

The coating layer capacities determined [in % of the theoreticalcapacity of the negative electrode] are 7.83% in electrolyte 1, 17.77%in electrolyte 4 and 20.02% in electrolyte 3. Even with the somewhathigher values of the coating layer capacity in electrolytes 3 and 4, abattery cell can be operated very well using these electrolytes incombination with the possibility of using high-voltage cathodes up to 5volts.

For the discharge experiments, three test full cells according toExample 3 were filled with electrolytes 1, 3 and 4 described in Example2. The test full cells had lithium nickel manganese cobalt oxide (NMC)as the active material of the positive electrode. To determine thedischarge capacities (see Example 4), the test full cells were chargedwith a current intensity of 15 mA up to a capacity of 125 mAh. Thedischarge then took place with a current intensity of 15 mA up to adischarge potential of 2.5 volts.

FIG. 12 shows the potential profile during the discharge over thedischarged amount of charge in % [% of the maximum charge (discharge)].All test full cells show a flat discharge curve, which is necessary forgood operation of a battery cell.

Experiment 6: Determination of the Conductivities of Electrolytes 1, 3and 4

To determine the conductivity, electrolytes 1, 3 and 4 were preparedusing different concentrations of compounds 1, 3 and 4. Theconductivities of the electrolytes were determined using a conductivemeasurement method for each concentration of the various compounds.After temperature control, a two-electrode sensor was held touching inthe solution and measured in a measuring range of 0-50 mS/cm. During themeasurements, it was noted that the sensor can react with theSO₂-containing electrolyte solution.

FIG. 13 shows the conductivity of electrolyte 1 as a function of theconcentration of compound 1. A maximum of the conductivity can be seenat a concentration of compound 1 of 0.6 mol/L-0.7 mol/L having a valueof approx. 37.9 mS/cm. In comparison, the organic electrolytes knownfrom the prior art, such as LP30 (1 M LiPF₆/EC-DMC (1:1 weight)) have aconductivity of only approx. 10 mS/cm.

FIG. 14 (electrolyte 3) and FIG. 15 (electrolyte 4) show theconductivity values determined for the different concentrations. Withelectrolyte 4, a maximum of 18 mS/cm is achieved at a conducting saltconcentration of 1 mol/L. Electrolyte 3 shows its highest conductivityof 0.5 mS/cm at a conducting salt concentration of 0.6 mol/L. Althoughelectrolyte 3 shows a lower conductivity, as in experiment 4, chargingor discharging of a test full cell is quite possible.

Experiment 7: Low Temperature Behavior

Two test full cells according to example 3 were produced in order todetermine the low-temperature behavior of electrolyte 1 in comparison tothe reference electrolyte. One test full cell was filled with referenceelectrolyte of the composition LiAlCl₄*6SO₂ and the other test full cellwith electrolyte 1. The test full cell having the reference electrolytecomprised lithium iron phosphate (LEP) as the active material, the testfull cell having electrolyte 1 comprised lithium nickel manganese cobaltoxide (NMC) as the active material of the positive electrode. The testfull cells were charged to 3.6 volts (LEP) or 4.4 volts (NMC) at 20° C.and discharged again to 2.5 volts at the respective temperature to beinvestigated. The discharge capacity reached at 20° C. was rated as100%. The temperature for the discharge was lowered in temperature stepsof 10° K. The discharge capacity obtained was described in % of thedischarge capacity at 20° C. Since the low-temperature discharges arealmost independent of the active materials used for the positive andnegative electrodes, the results can be transferred to all combinationsof active materials. Table 5 shows the results.

TABLE 5 Discharge Capacities as a Function of the Temperature DischargeDischarge Capacity of Capacity of Electrolyte Reference Temperature 1Electrolyte   20° C. 100% 100%   10° C.  99%  99%    0° C.  95%  46%−10° C.  89%  21% −20° C.  82% n/a −30° C.  73% n/a −35° C.  68% n/a−40° C.  61% n/a

The test full cell having electrolyte 1 shows very good low-temperaturebehavior. At −20° C., 82% of the capacity is reached, at −30° C., 73%.Even at a temperature of −40° C., 61% of the capacity can still bedischarged. In contrast, the test full cell having the referenceelectrolyte only shows a discharge capacity down to −10° C. A capacityof 21% is achieved here. The cell having the reference electrolyte canno longer be discharged at lower temperatures.

While exemplary embodiments have been disclosed hereinabove, the presentinvention is not limited to the disclosed embodiments. Instead, thisapplication is intended to cover any variations, uses, or adaptations ofthis disclosure using its general principles. Further, this applicationis intended to cover such departures from the present disclosure as comewithin known or customary practice in the art to which this inventionpertains and which fall within the limits of the appended claims.

What is claimed is:
 1. A rechargeable battery cell, comprising: anactive metal; at least one positive electrode comprising a compound inthe form of a layered oxide as an active material; at least one negativeelectrode; a housing; an SO₂ based electrolyte having at least one firstconducting salt which has the formula (I):

wherein: M is a metal selected from the group consisting of alkalimetals, alkaline earth metals, metals of group 12 of the periodic tableof the elements, and aluminum; x is an integer from 1 to 3; R¹, R², R³and R⁴ are selected independently of one another from the groupconsisting of C₁-C₁₀ alkyl, C₂-C₁₀ alkenyl, C₂-C₁₀ alkynyl, C₃-C₁₀cycloalkyl, C₆-C₁₄ aryl and C₅-C₁₄ heteroaryl; and Z is aluminum orboron.
 2. The rechargeable battery cell according to claim 1, whereinthe compound has the composition A_(x)M′_(y)M″_(z)O_(a), wherein: A isat least one metal selected from the group consisting of the alkalimetals, the alkaline earth metals, the metals of group 12 of theperiodic table and aluminum; M′ is at least one metal selected from thegroup consisting of the elements Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn;M″ is at least one element selected from the group consisting of theelements of groups 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 and 16of the periodic table of the elements; x and y independently of oneanother are numbers greater than 0; z is a number greater than or equalto 0; and a is a number greater than
 0. 3. The rechargeable battery cellaccording to claim 2, wherein the compound has the compositionA_(x)M′_(y)M″_(z)O_(a), in which A is lithium and M′ is cobalt.
 4. Therechargeable battery cell according to claim 3, wherein x and y areequal to 1, z is equal to 0, and a is equal to
 2. 5. The rechargeablebattery cell according to claim 2, wherein the compound has thecomposition A_(x)M′_(y)M″_(z)O_(a), in which A is lithium, M′ comprisesnickel and manganese and M″ is cobalt.
 6. The rechargeable battery cellaccording to claim 5, wherein the compound has the compositionLi_(x)Ni_(y1)Mn_(y2)Co_(z)O_(a), wherein x, y1 and y2 are, independentlyof one another, numbers greater than 0 and z is a number greater than orequal to 0 and a is a number greater than
 0. 7. The rechargeable batterycell according to claim 6, wherein the compound has the compositionLiNi_(0.33)Mn_(0.33)Co_(0.33)O₂, LiNi_(0.5)Mn_(0.3)Co_(0.2)O₂,LiNi_(0.5)Mn_(0.25)Co_(0.25)O₂, LiNi_(0.52)Mn_(0.32)Co_(0.16)O₂,LiNi_(0.55)Mn_(0.30)Co_(0.15)O₂, LiNi_(0.58)Mn_(0.14)Co_(0.28)O₂,LiNi_(0.6)Mn_(0.2)Co_(0.2)O₂, LiNi_(0.64)Mn_(0.18)Co_(0.18)O₂,LiNi_(0.65)Mn_(0.27)Co_(0.08)O₂, LiNi_(0.7)Mn_(0.2)Co_(0.1)O₂,LiNi_(0.7)Mn_(0.15)Co_(0.15)O₂, LiNi_(0.72)Mn_(0.10)Co_(0.18)O₂,LiNi_(0.76)Mn_(0.14)Co_(0.10)O, LiNi_(0.8)Mn_(0.1)Co_(0.1)O₂,LiNi_(0.86)Mn_(0.04)Co_(0.10)O₂, LiNi_(0.90)Mn_(0.05)Co_(0.05)O₂,LiNi_(0.95)Mn_(0.025)Co_(0.025)O₂ or a combination thereof.
 8. Therechargeable battery cell according to claim 2, wherein the compound hasthe composition Li_(x)Mn_(y)M″_(z)O_(a), wherein x is a number greaterthan or equal to 1 and y is a number greater than the number z.
 9. Therechargeable battery cell according to claim 8, wherein the compound hasthe composition Li_(x)Mn_(y)M″_(z)O_(a), in which M″ is nickel and/orcobalt.
 10. The rechargeable battery cell according to claim 9, whereinthe compound has the composition Li_(1.2)Mn_(0.525)Ni_(0.175)Co_(0.1)O₂,Li_(1.2)Mn_(0.6)Ni_(0.2)O₂, Li_(1.16)Mn_(0.61)Ni_(0.15)Co_(0.16)O₂ orLi_(1.2)Mn_(0.54)Ni_(0.13)Co_(0.13)O.
 11. The rechargeable battery cellaccording to claim 1, wherein R¹, R², R³ and R⁴ of the first conductingsalt are selected independently of one another from the group consistingof: C₁-C₆ alkyl; C₂-C₆ alkenyl; C₂-C₆ alkynyl; C₃-C₆ cycloalkyl; phenyl;and C₅-C₇ heteroaryl.
 12. The rechargeable battery cell according toclaim 11: wherein the C₁-C₆ alkyl is selected from the group consistingof C₂-C₄ alkyl, alkyl groups 2-propyl, methyl and ethyl; wherein theC₂-C₆ alkenyl is selected from the group consisting of C₂-C₄ alkenyl,ethenyl and propenyl; and wherein the C₂-C₆ alkynyl comprises C₂-C₄alkynyl.
 13. The rechargeable battery cell according to claim 1, whereinat least one of R¹, R², R³ and R⁴ of the first conducting salt issubstituted by at least one fluorine atom and/or by at least onechemical group, wherein the chemical group is selected from the groupconsisting of C₁-C₄ alkyl, C₂-C₄ alkenyl, C₂-C₄ alkynyl, phenyl andbenzyl.
 14. The rechargeable battery cell according to claim 1, whereinat least one of R¹, R², R³ and R⁴ of the first conducting salt is a CF₃group or an OSO₂CF₃ group.
 15. The rechargeable battery cell accordingto claim 1, wherein the first conducting salt is selected from the groupconsisting of:


16. The rechargeable battery cell according to claim 1, wherein theelectrolyte comprises a second conducting salt different from the firstconducting salt according to formula (I).
 17. The rechargeable batterycell according to claim 16, wherein the second conducting salt is analkali metal compound.
 18. The rechargeable battery cell according toclaim 17, wherein the second conducting salt comprises a lithiumcompound selected from the group consisting of an aluminate, a halide,an oxalate, a borate, a phosphate, an arsenate and a gallate.
 19. Therechargeable battery cell according to claim 16, wherein the secondconducting salt is a lithium tetrahaloaluminate.
 20. The rechargeablebattery cell according to claim 19, wherein the second conducting saltis lithium tetrachloroaluminate.
 21. The rechargeable battery cellaccording to claim 1, wherein the electrolyte comprises at least oneadditive.
 22. The rechargeable battery cell according to claim 21,wherein the additive of the electrolyte is selected from the groupconsisting of vinylene carbonate and its derivatives, vinylethylenecarbonate and its derivatives, methylethylene carbonate and itsderivatives, lithium (bisoxalato)borate, lithiumdifluoro(oxalato)borate, lithium tetrafluoro(oxalato)phosphate, lithiumoxalate, 2-vinylpyridine, 4-vinylpyridine, cyclic exomethylenecarbonates, sultones, cyclic and acyclic sulfonates, acyclic sulfites,cyclic and acyclic sulfinates, organic esters, inorganic acids, acyclicand cyclic alkanes, which acyclic and cyclic alkanes have a boilingpoint of at least 36° C. at 1 bar, aromatic compounds, halogenatedcyclic and acyclic sulfonylimides, halogenated cyclic and acyclicphosphate esters, halogenated cyclic and acyclic phosphines, halogenatedcyclic and acyclic phosphites, halogenated cyclic and acyclicphosphazenes, halogenated cyclic and acyclic silylamines, halogenatedcyclic and acyclic halogenated esters, halogenated cyclic and acyclicamides, halogenated cyclic and acyclic anhydrides, and halogenatedorganic heterocycles.
 23. The rechargeable battery cell according toclaim 1, wherein the electrolyte comprises: (i) 5 to 99.4% by weightsulfur dioxide, (ii) 0.6 to 95% by weight of the first conducting salt,(iii) 0 to 25% by weight of the second conducting salt, and (iv) 0 to10% by weight of the additive, based on the total weight of theelectrolyte composition.
 24. The rechargeable battery cell according toclaim 1, wherein the molar concentration of the first conducting salt isin a range based on the total volume of the electrolyte selected fromthe group consisting of from 0.01 mol/L to 10 mol/L, from 0.05 mol/L to10 mol/L, from 0.1 mol/L to 6 mol/L and from 0.2 mol/L to 3.5 mol/L. 25.The rechargeable battery cell according to claim 1, wherein theelectrolyte comprises SO₂ in the amount selected from the groupconsisting of at least 0.1 mol SO₂, at least 1 mol SO₂, at least 5 molSO₂, at least 10 mol SO₂ and at least 20 mol SO₂ per mole of conductingsalt.
 26. The rechargeable battery cell according to claim 1, whereinthe active metal is selected from the group consisting of an alkalimetal, an alkaline earth metal, a metal from group 12 of the periodictable and aluminum.
 27. The rechargeable battery cell according to claim26, wherein the alkali metal is lithium or sodium, the alkaline earthmetal is calcium, and the metal selected from group 12 of the periodictable is zinc.
 28. The rechargeable battery cell according to claim 1,wherein the negative electrode is an insertion electrode.
 29. Therechargeable battery cell according to claim 28, wherein insertionelectrode comprises carbon as the active material.
 30. The rechargeablebattery cell according to claim 29, wherein insertion electrodecomprises allotrope graphite.
 31. The rechargeable battery cellaccording to claim 1, wherein the positive electrode and/or the negativeelectrode have a discharge element, which is formed either planar in theform of a metal sheet or a metal foil, or three-dimensional in the formof a porous metal structure.
 32. The rechargeable battery cell accordingto claim 31, wherein the porous metal structure comprises a metal foam.33. The rechargeable battery cell according to claim 1, wherein thepositive electrode and/or the negative electrode comprises a fluorinatedbinder, or a binder consisting of a polymer which is built up frommonomeric structural units of a conjugated carboxylic acid or from thealkali, alkaline earth or ammonium salt of said conjugated carboxylicacid or from a combination thereof, or a binder consisting of a polymerbased on monomeric styrene and butadiene structural units, or a binderfrom the group of carboxymethyl celluloses, wherein the binder ispresent in a concentration selected from the group consisting of at most20% by weight, at most 15% by weight, at most 10% by weight, at most 7%by weight, at most 5% by weight and at most 2% by weight based on thetotal weight of the positive electrode.
 34. The rechargeable batterycell according to claim 33, wherein the binder comprises the fluorinatedbinder and the fluorinated binder is polyvinylidene fluoride and/or aterpolymer made of tetrafluoroethylene, hexafluoropropylene andvinylidene fluoride.
 35. The rechargeable battery cell according toclaim 1, wherein the at least one negative electrode comprises aplurality of negative electrodes and the at least one positive electrodecomprises a plurality of positive electrodes, wherein the negative andpositive electrodes are stacked alternately in the housing.
 36. Therechargeable battery cell according to claim 35, wherein the positiveelectrodes and the negative electrodes are each electrically separatedfrom one another by separators.